Cellulose gel for 3d-objects

ABSTRACT

The present invention relates generally to the field of three-dimensional cellulose-based objects, for example cellulose base packaging materials. In particular, the present invention relates to molded cellulose-based objects with a functionalized surface, for example a surface that reduces water absorption. One embodiment of the present invention relates to a molded cellulose-based object comprising a cellulose gel layer. For example, the cellulose gel layer may be obtained by sulfurization.

The present invention relates generally to the field of three-dimensional cellulose-based objects, for example cellulose based packaging materials. In particular, the present invention relates to molded cellulose-based objects with a functionalized surface, for example a smoother surface that reduces water absorption. One embodiment of the present invention relates to a molded cellulose-based object comprising a cellulose gel layer. For example, the cellulose gel layer may be obtained by sulfurization.

Packaging of manufactured food products is a vital part of the food industry today as it ensures food safety, preserves food quality and plays an important role in production processes, in brand communication and in digitalization. Indeed, several studies show that for a large part of consumers the packaging of a product is one key aspect that drives the purchase decision.

Plastic packaging is used frequently in the economy and in people's daily lives. It has multiple advantages, such as its flexibility and its light weight. Such a weight reduction contributes to fuel saving and CO₂ reduction during transport, for example. Its barrier properties help to reduce food waste due a positive effect on increasing shelf life. The barrier properties also help to secure food safety.

However, according to the European strategy for plastics in a circular economy, recently published by the European Commission, around 25.8 million tons of plastic waste are generated in Europe every year with less than 30% of such waste being collected for recycling and between 150 000 to 500 000 tons of plastic waste entering the oceans every year.

One of the main problems associated with packaging in general is the generation of packaging waste. According to Eurostat in 2017, 172.6 kg of packaging waste was generated per inhabitant in the EU.

The industry addresses this issue by embracing the circular economy. In line with this, the European Commission has recently communicated a new Circular Economy Action Plan (COMMUNICATION FROM THE COMMISSION TO THE EUROPEAN PARLIAMENT, THE COUNCIL, THE EUROPEAN ECONOMIC AND SOCIAL COMMITTEE AND THE COMMITTEE OF THE REGIONSA new Circular Economy Action Plan For a cleaner and more competitive Europe, Brussels, Nov. 3, 2020). Accordingly, the EU needs to accelerate the transition towards a regenerative growth model that gives back to the planet more than it takes, advance towards keeping its resource consumption within planetary boundaries, and therefore strive to reduce its consumption footprint and double its circular material use rate in the coming decade.

To ensure that, e.g., plastic waste is reduced, significant efforts are made in the industry and in commerce. Replacing plastics with paper in food packaging is not an easy task. A change in packaging material must not compromise consumer safety. The packaging must serve to protect the food, but must also be robust enough to be handled by machines during the production process, and must allow that the food product is presented effectively.

One step towards meeting the challenges mentioned above is to use cellulose-based packaging material. However, cellulose based packaging materials are typically porous and absorb liquids, such as water or oil, for example, very well. This makes many cellulose-based packaging materials unsuitable for food products.

One way to address this is to use multi-layer paper-based materials. The necessity to use multiple layers, however, reduces the cellulose content of the packaging material.

Further, surface modification for cellulose-based papers is usually provided by using roll-to-roll processes. These processes are not available for three-dimensional processes. As a result, solutions that are known for paper, for example sulfurization of papers, known from baking paper, for example, are unavailable for three dimensional cellulose based objects.

Furthermore, 3D cellulose based packaging materials usually have rough surfaces, even rougher than paper. As a result, the use of large amounts of surface coating material is usually necessary.

Consequently, there is a need in the art for three-dimensional cellulose-based objects that are resistant against liquid absorption or/or smooth enough for a second coating that uses small amounts of coating, so that they can be used as packaging material, for example food packaging material, that have an as high cellulose content as possible and that can be recycled with the paper or carton stream.

Any reference to prior art documents in this specification is not to be considered an admission that such prior art is widely known or forms part of the common general knowledge in the field.

The objective of the present invention was it to enrich or improve the state of the art and in particular to provide three-dimensional cellulose-based objects that are resistant against liquid absorption so that they can be used as packaging material, for example food packaging material, that have an as high cellulose content as possible and that can be recycled with the paper or carton stream, and/or that have a smooth surface that allows for polymer coating with small amounts of coating material, or to at least provide a useful alternative to solutions existing in the art.

The inventors were surprised to see that the objective of the present invention could be achieved by the subject matter of the independent claims. The dependent claims further develop the idea of the present invention.

Accordingly, the present invention provides a moulded cellulose-based object comprising a cellulose gel layer.

As used in this specification, the words “comprises”, “comprising”, and similar words, are not to be interpreted in an exclusive or exhaustive sense. In other words, they are intended to mean “including, but not limited to”.

The present inventors have shown that it is possible to produce a three-dimensional, for example a moulded cellulose based object with a dried cellulose gel layer, so that the dried cellulose gel layer provides the three-dimensional cellulose based object with a liquid repellence, for example a water repellence and/or an oil repellence. Using a cellulose gel layer to functionalize the surface of the three-dimensional cellulose-based object has the advantage that the cellulose content of the cellulose-based object can be very high. This in turn ensures that the moulded cellulose-based object can be recycled with the paper or the carton stream. This dried cellulose gel also provides a smoother and non-porous surface, useful for an additional coating on the surface of such 3D molded pulp.

FIG. 1 shows a surface view of a treated sample obtained with a Scanning Electronic Microscope (SEM). A homogenous cellulose gel layer can be observed.

FIG. 2 shows a side view of a cut sample allowing a rough estimation of the cellulose gel layer thickness. The image was obtained with a Scanning Electronic Microscope (SEM).

FIG. 3 shows the surface of molded cellulose before (left) and after (right) the treatment to have cellulose gel at the surface. The images were obtained with a Scanning Electronic Microscope (SEM).

Consequently, the present invention relates in part to a moulded cellulose-based object comprising a dried cellulose gel layer. The moulded cellulose-based object may be a three-dimensional object.

For the purpose of the present invention, a three-dimensional object may be an object where one dimension is not significantly smaller than the other two dimensions. For example, in a three dimensional object on dimension may have a length of not less than about 5% of the other two dimensions, not less than about 5% of the other two dimensions, not less than about 10% of the other two dimensions, not less than about 15% of the other two dimensions, not less than about 20% of the other two dimensions, not less than about 25% of the other two dimensions, not less than about 30% of the other two dimensions, not less than about 35% of the other two dimensions, or not less than about 40% of the other two dimensions.

According to DE69617553T2, it is well-known to dip paper into sulfuric acid to make the paper impermeable for fat and resistant towards defibrillation through water. In this case, it is a roll to roll process of flexible 2D materials and the sulfurization occurs on the entire paper thickness creating a composite of cellulose fibre with cellulose gel (well known as vegetable parchment) but which is not anymore recyclable.

The inventors have found with a 3D molded cellulose-based object that a cellulose gel can be formed only at the surface of the molded cellulose-based object. A drying step will result in a water and oil repellent smoother surface of the molded cellulose-based object.

The gel can, for example, be generated by dipping the molded cellulose-based object into an acid, for example sulfuric acid. Without wishing to be bound by theory, the inventors presently believe that the free hydroxyl groups of the cellulose react with the acid, swelling/dissolving a layer of the depolymerized cellulose. This layer of cellulose can be reprecipitated in form of amorphous cellulose (cellulose II) as a gel, for example, by washing the molded cellulose-based object that was subjected to an acid with water.

Finally, the resulting molded cellulose-based object comprising the cellulose gel layer can be dried. A moulded cellulose-based object comprising a dried cellulose gel layer results.

Hence, for example, the dried cellulose gel layer of the moulded cellulose-based object in accordance with the present invention may be obtained by using solubilization/reprecipitation process. The solubilization/reprecipitation process may be carried out with sulfuric acid, for example.

Hence, one embodiment of the present invention relates to a moulded cellulose-based object comprising a sulfurization layer. The sulfurization layer may be a cellulose gel formed by the treatment of cellulose with sulfuric acid, followed by a washing step and drying step.

In accordance with the present invention, any moulded cellulose-based object may be provided with a dried cellulose gel layer. As the dried cellulose layer is very efficient in providing a lipid barrier and/or a liquid barrier, for example a water barrier, to the cellulose-based object, such a dried cellulose gel layer is for example very useful, if the moulded cellulose-based object is a packaging, for example a packaging for food products. In particular it is useful for packaging for food products that have a lipid and/or liquid content.

The moulded cellulose-based object may be packaging selected from the group consisting of primary packaging, secondary packaging and tertiary packaging. A primary packaging for a food product may be a packaging for a food product that is in direct contact with the actual food product. A secondary packaging for a food product may be a packaging for a food product that helps secure one or more food products contained in a primary packaging. A secondary material is typically used when multiple food products are provided to consumers in a single container. A tertiary packaging for a food product may be a packaging for a food product that helps secure one or more food products contained in a primary packaging and/or in a primary and secondary packaging during transport.

The packaging may be any type of packaging. The inventors propose, in particular, that the packaging may be selected from the group consisting of cups, bottles, trays, capsules, straws, spoons, tips and lids.

Moulded cellulose-based objects are usually prepared from cellulose-based pulps, which are then thermoformed into cellulose-based objects. For example, the cellulose based pulps may contain different types of cellulose pulps. Hence, the cellulose-based object may comprise comprises cellulose pulp selected from the group consisting of mechanical pulp, recycled paper pulp, bagasse pulp, annual plant pulp, virgin cellulose pulp, refined cellulose pulp, or a combination thereof. The cellulose-based object may also consist of cellulose pulp selected from the group consisting of mechanical pulp, recycled paper pulp, bagasse pulp, annual plant pulp, virgin cellulose pulp, refined cellulose pulp, or a combination thereof.

The inventors have produced a very good prototype using kraft bleached cellulose. Hence, the moulded cellulose-based object in accordance with the present invention may comprise or consist of kraft bleached cellulose.

The cellulose-based object, for example the cellulose-based pulp may also contain a sizing agent. Sizing agents are well-known in the art. Alkylketene dimer (AKD) and alkenyl succinic anhydride (ASA) are typically used as sizing agents. The inventors have obtained particularly good results when alkylketene dimer (AKD) was used as sizing agent. Hence, the cellulose-based object in accordance with the present invention may further comprise AKD.

The dried cellulose gel may be the only “coating” layer on the moulded cellulose-based object.

For example, the dried cellulose gel layer may be on the inside of the moulded cellulose-based object in direct contact with a food product inside the moulded cellulose-based object.

The dried cellulose gel will provide a smooth and non-porous surface and which then may also be further treated by coating it with at least one further coating. This further coating may—for example—provide further barrier properties and/or certain desired optical properties. Hence, the dried cellulose gel on the moulded cellulose-based object may be a pre-treatment of the surface coated with at least one further coating.

In general, the thickness of the dried cellulose gel layer will have an influence on the barrier properties provided by the dried cellulose gel layer. Generally, a thicker gel layer will provide better barrier properties. However, the generation of a thick layer may also require significant gel formation, which may have an impact on the cellulose-based basis material and on the recyclability.

The inventors have obtained very good results, when the dried cellulose gel layer has a thickness in the range of about 2- to 80 μm, for example of about 5- to 60 μm or of about 10- to 30 μm.

The inventors were able to produce moulded cellulose-based objects with an excellent oil resistance, a low air permeability and/or a low water absorbance.

For example, the moulded cellulose-based object in accordance with the present invention may have oil resistance in the range of 10 to 12 in a kit test. The kit test is well accepted in the art and is, for example, described in Grease Resistance—Kit Test (TAPPI T559). The Kit test method describes a procedure for testing the degree of repellency of paper treated with sizing agents. This test was originally developed to know when fluorochemical was incorporated and the approximate level of grease resistance imparted. Testing uses a series of numbered reagents with various surface tension onto the surface of the sample. The solutions are numbered from 1 (the least aggressive) to 12 (the most aggressive). The highest numbered solution that does not stain the surface is reported as the “kit rating.”

Further, the moulded cellulose-based object in accordance with the present invention may have an air permeability in the range of 1 to 0.001 cm³/(m²·Pa·s).

Even further, the moulded cellulose-based object in accordance with the present invention may have a water absorbance in a 60 min Cobb test of below 100 g/m². The water absorbance of cellulose-based materials can be determined according to ISO 535.

Consequently, the moulded cellulose-based object in accordance with the present invention may have an oil resistance in the range of 10 to 12 in a kit test; an air permeability in the range of 1 to 0.001 cm³/(m²·Pa·s), and/or a water absorbance in the range of Cobb 60 min below 100 g/m².

wherein the moulded cellulose-based object has an oil resistance in the range of 10 to 12 in a kit test an air permeability in the range of 1 to 0.001 cm³/(m²·Pa·s), and/or water absorbance in the range of Cobb 60 min below 100 g/m².

The moulded cellulose-based object in accordance with the present invention may be prepared by applying a cellulose gel onto a cellulose-based moulded object and by washing and drying it.

The inventors have obtained particularly promising results when a strong acid, such as sulfuric acid, for example, was applied to the surface of the moulded cellulose-based object at low temperature. In a subsequent washing step, for example in cold water, the cellulose gel was formed on the surface of the moulded cellulose-based object. The resulting moulded cellulose-based object with a cellulose gel layer on its surface was then dried, for example by air drying or oven drying.

Hence, the moulded cellulose-based object in accordance with the present invention may be obtainable or obtained by a process comprising the steps of

-   -   a. dipping a moulded cellulose-based object into a H₂SO₄         solution,     -   b. washing the moulded cellulose-based object after dipping it         into a H₂SO₄ solution, and     -   c. drying the moulded cellulose-based object after dipping it         into a H₂SO₄ solution and washing it.

The H₂SO₄ solution may be an about 60-80 weight-% H₂SO₄ solution. The moulded cellulose-based object may be dipped into a H₂SO₄ solution at a temperature at about 3 to 30° C., and more preferably between 3 and 10° C. The dipping of the moulded cellulose-based object into a H₂SO₄ solution may be carried out for about 1 to 60 seconds. Hence the dipping of the moulded cellulose-based object into the H₂SO₄ solution may be carried out with an about 60-80 weight-% H₂SO₄ solution at a temperature of about 3 to 30° C. for about 1 to 60 seconds.

After dipping it into a H₂SO₄ solution the moulded cellulose-based object may be washed in a washing bath, for example a water bath, optionally assisted by scrubbing. Optionally, for example to ensure a more complete removal of free acid, the washed moulded cellulose-based object may be further washed in a second washing bath, for example a second water bath.

To obtain an excellent formation of a dried cellulose gel layer on the surface of the moulded cellulose-based object, the inventors have obtained very good results, when the drying step was carried out in an oven at elevated temperatures. Accordingly, the inventors recommend that the washed moulded cellulose-based object may be dried in an oven at a temperature in the range of about 50-180° C. this drying step is carried out until the moulded cellulose-based object is sufficiently dry.

Those skilled in the art will understand that they can freely combine all features of the present invention disclosed herein. In particular, features described for the product of the present invention may be combined with the use of the present invention and vice versa. Further, features described for different embodiments of the present invention may be combined.

Although the invention has been described by way of example, it should be appreciated that variations and modifications may be made without departing from the scope of the invention as defined in the claims.

Furthermore, where known equivalents exist to specific features, such equivalents are incorporated as if specifically referred in this specification. Further advantages and features of the present invention are apparent from the figures and non-limiting examples.

The sulfurization protocol is presented as follows:

Firstly, prepare a 72% in weight H₂SO₄ solution. Refrigerate the solution to a temperature around 10° C. Prepare at least 2 water bathes.

Dip the sample in the sulfuric acid for a few seconds (10-60 sec depending on sample wettability). After dipping, put the sample in a water bath and scrub vigorously inside water.

Put the sample in a 2nd water bath before rinsing the sample under flowing water for a few minutes. Dry the sample at 80° C. in an oven until it is dry. This procedure has been repeated at least 5 times to check the reproducibility of the treatment.

In this example one highly refined kraft bleached cellulose was tested. The molded pulp contains AKD, which lowers the wettability of the sample.

To assess if a cellulose gel layer has been formed, the sample is immerged in colored oil during 1 hour. The weak points, where no cellulose gel film was formed will get colored. In both cases, no more than 2 colored points of less than 0.5 cm² were obtained on a surface of 10 cm×10 cm and, for most of samples, even no points were visible proving the existence of the lipid/oil barrier.

Kit test were also performed following the standard Tappi T559.

The reference molded pulp has a very low value of 1 whereas the sulfurized molded pulp have a value between 9 and 11.

After treating samples as per the above protocol, a Cobb 60 seconds test was also performed according to ISO 535. Goal of this test is to assess the water absorbance during a given time on a normalized surface.

Results are summarized in the table below:

Cobb 60 sec - Cobb 60 sec - ref cellulose gel film High refined cellulose + 199 83 AKD

A significant decrease in water adsorption could be observed as evidenced by a change in average value from about 200 to about 80 g/m²·d.

Furthermore, the porosity—as measured by Bendtsen apparatus—of 5 different samples for which we have performed this treatment strongly decreases from about 145 to 5 ml/min as shown in the table below. This proves also the creation of this continuous cellulose gel film.

Before treatment After treatment

Porosity Porosity Air flow [ml/min] Air flow [ml/min] 154 10 145 2 142 5 147 5 139 7

This cellulose gel layer could also play the role of a pre-treatment which favour the deposition of a barrier layer dispersion. Indeed, the surface is already closed and smoother after the gel formation and it is easier to top coat a barrier layer on it. The coating layer is not anymore adsorbed by the porous molded cellulose.

As shown in the table below, the fact to have this sulfurized pretreatment clearly helps for the efficiency of a second coating layer. Each barrier coating is about 15 gsm. After one layer, we obtain a kit value of 1 without pretreatment whereas we can reach already 12 with only one barrier coating after the sulfurization pretreatment.

Without With 1x barrier With 2x barrier Samples/Kit test value coating coating coating Molded Pulp 1 1 3 Sulfurized Molded pulp 9 12 12 

1. Moulded cellulose-based object comprising a dried cellulose gel layer.
 2. Moulded cellulose-based object in accordance with claim 1, wherein the moulded cellulose-based object is packaging selected from the group consisting of primary packaging, secondary packaging and tertiary packaging.
 3. Moulded cellulose-based object in accordance with claim 1, wherein the packaging is selected from the group consisting of cups, bottles, trays, capsules, straws, spoon, tips and lids.
 4. Moulded cellulose-based object in accordance with claim 1, wherein the packaging is food packaging.
 5. Moulded cellulose-based object in accordance with claim 1, wherein the object comprises cellulose pulp selected from the group consisting of mechanical pulp, recycled paper pulp, bagasse pulp, annual plant pulp, virgin cellulose pulp, refined cellulose pulp, and a combination thereof.
 6. Moulded cellulose-based object in accordance with claim 1, wherein the dried cellulose gel on the moulded cellulose-based object is a pre-treatment of the surface coated with at least one further coating.
 7. Moulded cellulose-based object in accordance with claim 1, wherein the object further comprises alkyl ketene dimer (AKD).
 8. Moulded cellulose-based object in accordance with claim 1, wherein the dried cellulose gel layer has a thickness in the range of about 2- to 80 μm.
 9. Moulded cellulose-based object in accordance with claim 1, wherein the moulded cellulose-based object has an oil resistance in the range of 10 to 12 in a kit test an air permeability in the range of 1 to 0.001 cm³/(m²·Pa·s), and/or water absorbance in a 60 min Cobb test of below 100 g/m².
 10. Moulded cellulose-based object in accordance with claim 1, wherein the moulded cellulose-based object comprises highly refined kraft bleached cellulose.
 11. A process for making a moulded cellulose-based object comprising the steps of a. dipping a moulded cellulose-based object into a H₂SO₄ solution, b. washing the moulded cellulose-based object after dipping it into a H₂SO₄ solution, and c. drying the moulded cellulose-based object after dipping it into a H₂SO₄ solution and washing it.
 12. Moulded cellulose-based object in accordance with claim 11, wherein the H₂SO₄ solution is an about 60-80 weight-% H₂SO₄ solution at a temperature at about 3 to 30° C. for about 1 to 60 seconds.
 13. Moulded cellulose-based object in accordance with claim 11, wherein the moulded cellulose-based object after dipping it into a H₂SO₄ solution is washed in a water bath, optionally assisted by scrubbing.
 14. Moulded cellulose-based object in accordance with claim 11, wherein the washed moulded cellulose-based object is further washed in a second washing bath.
 15. Moulded cellulose-based object in accordance with claim 11, wherein the washed moulded cellulose-based object is dried in an oven at a temperature in the range of about 50-180° C. 